🔍 Key Concepts

• 2D position fix on the Earth’s surface (latitude and longitude) • How many independent lines of position (LOPs) are needed to pinpoint a location in two dimensions • Relationship between satellite ranges and position lines in GPS

💭 Think About

• If each measurement (or line of position) reduces your unknowns by one, how many do you need to solve for a position defined by latitude and longitude? • On a traditional paper chart, how many crossing lines of position are normally used to mark a reliable fix? • In GPS, think of each satellite giving you a circle of possible positions on the Earth’s surface; how many such circles must intersect to give a single point in 2D?

✅ Before You Answer

• Clarify that a two-dimensional fix means only horizontal position (lat/long), not altitude • Remember that each line of position eliminates one degree of freedom • Confirm how many unknowns you are solving for in a 2D horizontal fix